1. Field of the Invention
The present invention relates to a multi-layered aquaculture system which utilizes the methods and apparatuses for guiding aquatic crustaceans' locomotive orientation with their innate biological tendency responding to specific contrasts of bright and dark. This multi-layered aquaculture system also utilizes a means for arranging even water follow to efficiently promote the utilization of above-mentioned methods and apparatuses and at the same time facilitate the removal of physical or biological wastes from the water body of culture.
2. Description of Related Art
Aquatic crustaceans are important economic animals. People usually obtain those animals by harvesting them from nature environment directly or by artificial cultivation. Many countries have paid great attention to focus on this artificial cultivation. Traditionally, such artificial cultivation (named aquaculture) makes use of wide expanse of land and ponds with natural water supply. Recently, several automated high-density culturing systems have been disclosed. These systems use water recirculation equipments and filtering apparatuses to curtail both the consumption of water and land resources and the damages to the natural environment, like U.S. Pat. Nos. 4,368,691, 4,446,025 and 5,961,831. High-density cultivation systems bring larger profit margins but simultaneously increase the production loss resulting from cannibalization of animals densely living in the systems. This loss is derived from differences in size and living stage of cultured animals, ex. newly molted or immature crustaceans are usually vulnerable to predation of their none-molted and/or larger mates within the same body of water. This is the bottleneck in the efforts to elevate the culture density and hence to increase profits as well.
Cannibalism-avoiding behavioral management is thus an important task for maintaining cultivated aquatic crustaceans in above-said high-density systems. For that purpose, spatial separation of molting and none-molting crustaceans is one way to avoid molted animals from being predated. Several means to attract aquatic crustaceans' active moving can be employed in attempting to lure none-molting animals to stay away from molted ones. For example, traditional pond culture or tank culture uses deep water and wide space to passively reduce the contact between newly molted and none-molted crustaceans. In addition, scent/taste attractants and chemo-attractants are used to manage crustacean's displacement over feeding, breeding and hatching. U.S. Pat. No. 5,706,759 discloses a process to investigate potential chemo-stimulants, chemo-repelling agents or chemo-attractants for shrimps, but this invention still lacks further practical techniques for behavioral management in high-density culture. A kind of bait fluid, such as fish oil, is used in U.S. Pat. No. 4,828,829 for harvesting crab only with expected high efficiency. A food-luring trapper using an attractor to attract plankton or other similar shrimp food organisms is designed to allure and catch shrimp (U.S. Pat. No. 5,259,809). No other successful methods for managing the motion of aquatic crustaceans in the light of their biological responses reacting to bright and dark visual stimuli have been developed previously.
Due to lack of proper techniques for culturing and managing aquatic crustaceans in high densities, the newly developed re-circulation systems have culture densities always maintained as a balance between cannibalization and growth, and, in shrimp, the culture pond or tank is always kept in certain water depth, about 0.6 to 2.0 meter, in order to reduce the incidence of cannibalizing behavior basing on the behavior that newly molted shrimp jump back or up away in order to escape from the attack of other none-molted shrimp mates. The culture water body with the depth of 0.6 to 2.0 meters has too large a mass to enable the development of multi-layered culture system and thus the traditional culture system is restricted to a planar installation. In nature, many aquatic crustaceans, such as shrimps, inhabit in water environments with bright-dark alternating or contrasting light effects appearing as wavy light reflections in shelters and crevices but not in open fields. Crustaceans may use these light effects to aim for a potential hiding place. Once arriving to the location, they may use their other senses, such as tactile senses, to decide if they would take the action of hiding or go for another potential location.
Propensity to react to the bright and dark visual stimuli in aquatic crustaceans is a unique nature which can be used in a feasible means to guide their motion and localization. The present invention utilizes methods and apparatuses for guiding aquatic crustaceans, which is centered upon the aforesaid biological tendency, to overcome the serious problem of cannibalism encountered in the culture system which adopts shallow-water containers and further to increase efficiency of land use to almost 10 times or more by the construction of multi-layered aquaculture system. The present invention, a multi-layered shallow-water culture system installed with a water flow arrangement means to efficiently promote the utilization of above-mentioned methods and apparatuses and at the same time facilitate the removal of physical or biological wastes from the water body of culture. No practical concepts in the prior arts, however, are disclosed as an efficient and effective system for culturing aquatic crustaceans in this multi-layered style similar to the present invention.